In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) with one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio-network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio-network node. The radio-network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio-network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio-network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio-network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio-network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio-network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio-network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio-network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio-network nodes, this interface being denoted the X2 interface. EPS is the Evolved 3GPP Packet Switched Domain.
Advanced Antenna Systems (AASs) is an area where technology has advanced significantly in recent years and where we also foresee a rapid technology development in the years to come. Hence it is natural to assume that AASs in general and massive Multiple Input Multiple Output (MIMO) transmission and reception in particular will be a cornerstone in a future Fifth Generation (5G) system.
In relation to the AAS, beam-forming is becoming increasingly popular and capable and it is not only for transmission of data but also for transmission of control information. This is one motivation behind the control channel in LTE known as Enhanced Physical Downlink Control Channel (ePDCCH). When the control channel is beam-formed, the cost of transmitting the overhead control information can be reduced due to the increased link budget provided by the additional antenna gain.
Automatic repeat-request (ARQ) is an error-control technique used in many wireless networks. With ARQ, a receiver of data transmissions sends acknowledgements (ACKs) or negative acknowledgments (NACKs) to inform the transmitter of whether each message has been correctly received. Incorrectly received messages, as well as messages that aren't acknowledged at all, can then be re-transmitted.
Hybrid ARQ (HARQ) combines ARQ with forward error-correction (FEC) coding of the data messages, to improve the ability of the receiver to receive and correctly decode the transmitted messages. As with conventional ARQ, receivers employing HARQ send ACKs and NACKs, as appropriate, after each attempt to decode a message. These ACKs and NACKs are referred to as “HARQ feedback.”
For downlink HARQ transmissions in LTE today, HARQ feedback is sent from the wireless device, e.g. a User Equipment (UE) to the Network (NW) on either Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH), depending on whether the wireless device has been scheduled for uplink PUSCH transmission or not. The NW can thereafter, on an individual HARQ process basis, draw conclusions on whether the last HARQ reception for that process was successful or not, based on received ACK or NACK, or even if the Downlink (DL) Assignment reception failed, i.e. the wireless device does not send any feedback also called Discontinuous Transmission (DTX).
When accessing the wireless communication network the wireless device may transmit an access request on a physical random-access channel (PRACH). This channel is used to carry random access preambles used for initiation of a random-access procedure for accessing the radio-network node. The basic structure of a random access preamble comprises a Cyclic Prefix (CP), a sequence and a guard time. Preambles can be constructed in such a way that the processing in a PRACH receiver can utilize the same-length Fast Fourier Transformers (FFT) as for all other Uplink (UL) channels and signals. PRACH sequences may be constructed by repeating a short sequence (n) wherein a length of a short sequence equals a length of an Orthogonal frequency-division multiplexing (OFDM) symbol. Each short sequence may act as the CP for next short sequence, and the short sequence may be constructed by using Zadoff-Chu sequences, see FIG. 1a where a PRACH preamble is constructed with repeated short sequence. In the current 3GPP LTE standard, the Random Access (RA) preamble, also called PRACH preamble or just preamble, is much longer than one OFDM symbols so large FFT is needed at the receiver.
Allocating a certain preamble of the PRACH procedure where a given PRACH preamble is allocated with a static configured preamble length results in a solution that may have a poor performance of the wireless communication network. Using a long preamble results in more received signal energy with a good performance but with a lower capacity. Using a short preamble results in less received signal energy with higher capacity, but with worse performance.